Coverage dependence of glycine adsorption on the Ge(100)-2 x 1 surface

Abstract

A combination of infrared spectroscopy, X-ray photoelectron spectroscopy and density functional theory has been used to investigate the adsorption behavior of glycine at the Ge(100) - 2 x 1 surface under ultrahigh vacuum conditions. Comparison of experimental and simulated IR spectra indicates that at 310 K, glycine adsorbs on Ge(100) - 2 x 1 via O-H dissociation, with some fraction of the products also forming an N dative bond to a neighboring germanium atom. O-Ge dative bonding is not observed. As coverage increases, the surface concentration of the monodentate O-H dissociated adduct increases, while that of the N dativebonded species appears constant. XPS data support and clarify the IR findings and reveal new insights, including the presence at higher coverage of a minor product that has undergone dual O-H and N-H dissociation. These findings are supported by the calculated energy diagrams, which indicate that the reaction of a glycine molecule on the Ge(100) - 2 x 1 surface via O-H dissociation and interdimer N dative bonding is both kinetically and thermodynamically favorable and that N-H dissociation of this adduct is feasible at room temperature given incomplete thermal accommodation along the reaction pathway. (C) 2011 Elsevier B.V. All rights reserved.